XMM-Newton observations of the BL Lac MS 0205.7+3509: A dense, low-metallicity absorber

Free access article

Issue		A&A Volume 418, Number 2, May I 2004


Page(s)		459 - 463
Section		Extragalactic astronomy
DOI		http://dx.doi.org/10.1051/0004-6361:20034524

A&A 418, 459-463 (2004)
DOI: 10.1051/0004-6361:20034524

XMM-Newton observations of the BL Lac MS 0205.7+3509: A dense, low-metallicity absorber

D. Watson^{1, 2}, B. McBreen³, L. Hanlon³, J. N. Reeves^{4, 5}, N. Smith⁶, E. Perlman^{7, 8}, J. Stocke⁹ and T. A. Rector^{10, 11}

¹ Niels Bohr Institute, Astronomical Observatory, University of Copenhagen, Juliane-Maries Vej 30, 2100 Copenhagen Ø, Denmark
² X-Ray Astronomy Group, Department of Physics and Astronomy, Leicester University, Leicester LE1 7RH, UK
³ Dept. of Experimental Physics, University College Dublin, Dublin 4, Ireland
⁴ Laboratory for High Energy Astrophysics, Code 662, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
⁵ Universities Space Research Association
⁶ Dept. of Applied Physics and Instrumentation, Cork Institute of Technology, Cork, Ireland
⁷ Joint Center for Astrophysics, University of Maryland, Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250, USA
⁸ Johns Hopkins University, Baltimore, MD 21218, USA
⁹ Center for Astrophysics and Space Astronomy, University of Colorado, Boulder, CO 80309-0389, USA
¹⁰ National Optical Astronomy Observatory, 950 N. Cherry Ave., Tucson, AZ 85719, USA
¹¹ University of Alaska, 3211 Providence Dr., BMB 212, Anchorage, AK 99508, USA

(Received 20 June 2003 / Accepted 26 January 2004 )

Abstract
The high-frequency-peaked BL Lac, MS 0205.7+3509 was observed twice with XMM-Newton. Both X-ray spectra are synchrotron-dominated, with mean 0.2-10 keV fluxes of $2.80\pm0.01$ and $3.34\pm0.02\times10^{-12}$ erg cm ^-2 s ^-1. The X-ray spectra are well fit by a power-law with absorption above the Galactic value, however no absorption edges are detected, implying a low metallicity absorber ( $Z_{\sun} = 0.04^{+0.03}_{-0.01}$ ) or an absorber with redshift above one (best-fit z=2.1 for an absorber with solar abundances). In either case the absorbing column density must be ${\sim}9\times10^{21}$ cm ^-2. A new optical spectrum is presented, with a $\ion{Mg}{ii}$ absorption doublet detected at z=0.351, but no other significant features. The optical spectrum shows little reddening, implying a low dust to gas ratio in the absorber. MS 0205.7+3509 must therefore be viewed through a high column density, low-metallicity gas cloud, probably at z=0.351 and associated with the galaxy that has been shown to be within ${\sim}2$ ´´ of the BL Lac.

Key words: galaxies: BL Lacertae objects: individual: MS 0205.7+3509 -- galaxies: active -- X-rays: galaxies

Offprint request: D. Watson, darach@astro.ku.dk

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